Earthen pits are in widespread use in industry. These pits are useful for containing waste materials, cooling water, process brines, and other materials. Ground water pollutants from such pits potentially include soluble components present in the contained materials. For example, drilling fluid disposal pits have been found to contain significant levels of sodium, sulfate, chlorate, arsenic, barium, chromium, lead, zinc, and total organic carbon. The transport and fate of these constituents in the subsurface may involve several processes (adsorption, microbial degradation, ion exchange, chemical precipitation, particulate transport, and others). It is influenced by several variables (constituent type, soil type, oxidation-reduction conditions, pH and other environmental factors).
The rate of release of soluble chemical constituents from pits is largely controlled by the permeability of underlying strata or liner materials. Liners can be formed from man-made materials, natural clays, or by exploiting the sealing properties of the waste drilling muds themselves. Such liners are needed to ensure the integrity of the earthen pit.
Of critical importance is the necessity to construct the pit and liner to prevent leakage of pit contents and consequent potential contamination of the surrounding environment. Such liners are classifiable into membrane liners, recompacted soil liners, and admixed soil liners.
Membrane liners usually are constructed of fabric reinforced plastic. Important advantages of membrane liners include their ability to contain a wide variety of fluids and their high resistance to chemical and bacterial deterioration. Disadvantages include vulnerability to ozone and ultraviolet deterioration. Also, membrane liners are comparatively susceptible to laceration, abrasion and puncture, as well as cracking and creasing at low temperatures and to distortion at high temperatures. Membrane liners do not have the ability to absorb or attenuate potential pollutants that could leach if a puncture should occur.
Clay admixtures and recompacted soils are the most frequently used liner materials in oilfield pit construction. Recompacted soil liners are constructed by compacting native soils to reduce or eliminate pores which allow leaching. Such liners, unless carefully constructed, frequently are not effective, however, to prevent penetration and/or overflow of the liner by the pollutant and are relatively expensive to install. Accordingly, the art is in need of a liner for pits, such as oilfield disposal pits, which is capable of containing pollutants without failures and which is relatively inexpensive to install.
Applicant is not aware of any prior art which, in his judgment as one skilled in the art, would anticipate or render obvious the present invention; however, for the purposes of fully developing the background of the invention, and establishing the state of the requisite art, the following art is set forth: "How to Select an Effective Waste Pit Liner", Aston A. Hinds et al, Drilling, Jan./Feb. 1987; "Hydraulic Conductivity and Leachability of Waste Drilling Fluids", G. M. Deeley et al, Ninth Annual Energy Sources Technology Conference, New Orleans, La., Feb. 23-27, 1986.